Barack Obama, the US president, has urged world leaders to act quickly to fight global warming or face an "irreversible catastrophe".
Speaking before the United Nations summit on climate change, Obama emphasised the need for an international agreement on global warming before a UN summit in Copenhagen in December.
According to the Intergovernmental Panel on Climate Change (IPCC), global temperatures will increase by at least 1.1C during the course of this century.
Scientists say that arctic temperatures are higher than at any other time in the past 2,000 years.
And if nothing is done, experts believe that sea levels will rise by about 50cm in the next 40 to 100 years. That will put 92 million people at risk.
Mike Hanna reports on the climate summit at the UN in New York.
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